A U.S.-focused retirement, life insurance and reinsurance company is set to shift its regional office from Southborough to NB Development Group’s Boston Landing mixed-use development in Brighton, MA.

Founded at Goldman Sachs in 2004 and separated as an independent company in 2013, New York City-based Global Atlantic Financial Group will occupy 46,290 square feet across the top two floors at 20 Guest St., a 223,877-square-foot, 10-story office building…